Injection molding apparatus

ABSTRACT

A heated manifold system for use in the distribution of heated plastic resins to the various cavities of injection molds for thermoplastic materials. The manifold main structure consists of modular components of similar cross-section that are nested into each other by employing similar slots cut out at the points of intersection of components. The thermoplastic resin passages are bored longitudinally in each modular components, and transverse bores at each intersection provide resin passages between the longitudinal bores. The system includes heated nozzles which have slots to receive cartridge heaters and heater covers, also spring clips to retain the covers and heaters, which can rotate around the shank of the nozzle to allow easy replacement of the cartridge heaters in the event of failure. Internal sealed liquid-filled channels or highly conductive metal rods are used to equalize the temperature of the nozzle from one extremity to the other.

This invention relates generally to injection molding apparatus forproducing thermoplastic products, and more particularly to heatedmanifolds for distributing molten plastic material from a commoninjection port to the various cavities of a mold.

In conventional molding practice, plastic molding material is heated toits fluid condition and forced along passages from a supply port to thecavities of a mold.

A manifold is used for providing heated passages and conveying fluidresin from a common supply port to the nozzles feeding the cavities.

Manifolds have been made of a block of steel that is bored to providethe passages for the molding material. The manifold is heated byelectric heating elements in grooves or holes in the manifold's steelblock. The unitary block of steel securely contains the fluid in themanifold's passages, despite pressures of perhaps twenty thousand poundsper square inch. Where the passages extend from the bores of themanifold into the manifold's nozzles, the abutting surfaces of the partsare made flat with high precision and securely clamped together toprevent leaks. The same care in avoiding leaks must be observed wheretwo or more blocks are combined in a manifold.

An object of the invention is to provide a novel heated manifold whichcan be produced economically and quickly. More particularly, an objectof the invention is to provide a novel manifold that can be assembled ofinterlocking prefabricated standardized components requiring only minormachining.

A further object of the invention is to provide a system of componentsthat can be easily assembled to form a manifold that is easy tointegrate with an existing or new injection mold.

An additional object of the invention is to provide a heated manifold ofassembled components which is virtually leak-proof under high pressure.

An additional object of the invention is to provide a versatile systemfor constructing manifolds and conveying molten plastic resin to anumber of points in the mold, adaptable to form a manifold for either afew mold cavities or many.

One more object of the invention is to provide easy means for assemblingand disassembling the components of the manifold for the purpose ofcleaning, repairing and adjusting the whole or part of the manifold.

One more object of the invention is to provide a nozzle for injectingthe resin into the cavities of a mold which is easily and economicallyconstructed and serviced.

Yet another object of the invention is to provide a nozzle which isheated by electric heating elements and which contains temperatureaveraging means comprising channels filled with or largely filled withheat-transfer liquid or metal.

Novel injection-mold manifolds are described in detail below and shownin the accompanying drawings, as illustrative embodiments of variousaspects of the invention, for achieving the foregoing object and stillother objects of the invention.

In the first of these embodiments, a novel manifold is an assembly ofstandardized stock members which, with only limited machiningoperations, can be assembled into an endless variety of manifolds. Wheretwo such stock members form a joint in the manifold, they may havetransverse slots or notches cut in them, each slot having essentiallythe same width as the member that intersects it and a depth of half theheight of the component members' cross-section.

Each member has a portion of reduced-thickness at the bottom of thenotch. A straight bore extends along each member through its unnotchedportions. This longitudinal bore extends off-center in the unnotchedportions of each member. Where the slotted portions of the two membersare planes fitted into each other, the axes of the longitudinal bores ofthe two members are on different planes, cross bores in thereduced-thickness portions connect the longitudinal bores with eachother. The cross bores join the longitudinal bores of both members toconstitute a continuous passage for the resin. The same joint betweenany two members of the manifold can be repeated using additional slottedor notched stock members to form a manifold for many mold cavities. Both"T" shaped junctions and "X" shaped passage junctions can beconstituted.

There is a danger of high-pressure fluid material leaking at thejunction of the bores of two assembled members of a manifold. Thisconcern is met introducing a seal between two assembled parts. The sealseats in a counterbore, the ends of the seal bearing against abuttingsurfaces of the assembled members.

In a preferred embodiment of the invention, the manifold is constructedof elongated members having identical cross-section. At the points wheretwo of the members intersect, identical slots are machined of one halfthe member's thickness; the width of the slot in each member equals thewidth of the other member. The reduced-thickness portion of each memberis fitted into the notch of the other member. The resulting structure isself supporting, relatively rigid, and all members become nested intoeach other. The upper and lower surfaces of the intersecting members arein parallel planes, being the upper and lower surfaces of the manifold.

The longitudinal bore in each member is plugged at the ends. Cross boresat the abutting surfaces of the notches form communicating channelsbetween the lengthwise bores of the members. The bottom surfaces of thenotches abut each other and are held under pressure by suitablefastners. Seals may be placed in recesses provided between the surfacesto ensure that no leaks of resin occur. In addition to the fastners, themembers may be forced against each other by the clamping action of themold and the back plate, which apply constant pressure against thesemold members wherever they form an intersection.

Each of the end plugs in the bores has an inclined surface at the backof the head. The plugs are held in place and they are prevented fromrotating by a dowel pin, which has an inclined surface at an anglematching the back of the head's angle. The pin is driven through a crosshole which is at right angles to the plugs. The dowel is kept fromloosening by a setscrew.

As one embodiment of a manifold, two sets of heating elements are placedin channels which are machined on the outer surfaces alongside theentire periphery of the manifold and are held in place by malleablemetal heater covers. One set of heaters is placed at the top, of eachmember of the manifold and one set at the bottom surface of each member;the heating elements are normally regulated individually to maintain themanifold at the proper temperature, by well known means.

In another embodiment of the invention, individual heating elements areplaced only on one side of each member of the manifold, namely theirunnotched sides, opposite the interlocking notches. In this way, eachmember of the manifold can be disassembled for repair, cleaning orheater replacement without disturbing the rest of the components or theheating elements. Each member of this manifold has a straightlongitudinal bore. The bore extends through the reduced-thicknessportion of each member; the bore extends in each member closer to itsunnotched surface than to its notched surface.

The heated nozzles are made of high strength steel and they are clampedbetween the manifold and each of the mold cavities. The heating elementsof the nozzles are of the cartridge type and in the illustratedembodiment they are placed in two channels 180 degrees apart, formedalongside the body or stem of the nozzle. The heating elements areparallel to the resin passage and held snugly in place by removableheater covers. The heater covers transfer heat from the outer surfacesof the heating elements back to the body of the nozzle. The heatercovers and the heater elements are pressed toward the body of the nozzleby spring retainers.

In order to equalize the temperature along its entire length, the nozzlehas bores which in the illustrative nozzles are located at 90 degreesfrom the heater channel and parallel to the resin passage in the nozzle.In one embodiment of the novel nozzles these bores are filled with aliquid such as water, then sealed. The liquid should have good heattransfer properties. The liquid cools the hotter sections of the nozzleand by conduction, convection and agitation transfers the heatlengthwise of the nozzle to cooler areas of the nozzle shank.

Heater retainers extend incompletely around the nozzle. If a cartridgeheater of the nozzle needs replacement, retainers are rotated around thenozzle to align the openings or gaps of the retainers with the heaterchannel. The heater cover is then free to be lifted, releasing theheater for replacement.

In another embodiment of the invention, solid rods of highly conductivemetal such as copper or silver, occupy the cavities of the nozzle as analternate means to produce an averaging effect for maintaining uniformtemperature along the nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and aspects of the invention will bebetter appreciated from the following detailed description ofillustrative apparatus embodying one of various aspects of theinvention, reference being made in the description to the accompanyingdrawings. In the drawings:

FIG. 1 is a section of a typical molding apparatus incorporating a novelmanifold and nozzle system as viewed in the planes designated A--A inFIG. 2.

FIG. 2 is an exploded perspective view of the manifold system in FIG. 1,portions of this manifold system being omitted for clarity.

FIG. 3 is a perspective view of an alternative form of the manifold inFIG. 2.

FIG. 4 is an exploded perspective of the manifold in FIG. 1, portionsbeing broken away and shown in cross-section.

FIG. 5 is a fragmentary cross-section of a joint of the manifold inFIGS. 2-4, as seen at the plane I--I of FIG. 3.

FIG. 6 is a fragmentary perspective of one end of a stock component ofthe manifold.

FIG. 7 is a fragmentary perspective cross-section taken along planeII--II of FIG. 6.

FIG. 8 is a perspective view of the nozzle in FIG. 2 with a portionsectioned off along the intersecting planes V--V to show the internalfeatures of the nozzle.

FIG. 9 is a fragmentary section of a nozzle as in FIG. 2 taken along theplane III--III of FIG. 2 showing a modification of the nozzle FIG. 8.

FIG. 10 is a cross-section of a nozzle as in FIG. 2 taken along theplane IV--IV of FIG. 2.

FIG. 11 is a cross-section of the nozzle of FIG. 2 like FIG. 10 but withthe parts in another relationship.

FIG. 12 is a cross-section of a modification of a nozzle in FIG. 2 takenalong the plane IV--IV.

FIG. 13 is the same as FIG. 12 showing a retaining "C" clip aligned forremoval of the heater.

FIG. 14 is a fragmentary section along plane II--II of one end of astock component of the manifold in FIG. 6.

Referring to FIG. 1 of the drawings, a manifold assembly 1 is clampedagainst nozzles 2 between a multi-cavity mold 3 and a back plate 4. Themanifold is kept from contacting the back plate by insulator spacers 5.Spacer blocks 6 separate back plate 4 from plate 3 of the two-part moldspacer blocks 6 are not so wide as to prevent the manifold and thenozzles from being forcefully clamped together between the back plate 4and part 3 of the mold. The back plate is fastened to mold 3 by asuitable number of screws 7. In operation, plastic resin is introducedby a supply nozzle 9, which is part of an injection mold press notshown, and it travels through passage 10 of the manifold and passage 11of the nozzles to fill the cavities 8. The resin is solidified in thecavities and parts 12 are ejected when the core side 13 of the mold isseparated.

The manifold 1 of FIGS. 2 and 4 and the manifold 1 of FIG. 3 areconstructed using three members M and three members M' of essentiallyidentical rectangular cross-section. These members M and M' can beroutinely prefabricated to accurate dimensional standards and later cutto required lengths. They may be modified to make manifolds of variousdimensions and configurations. The components in FIG. 3 have primednumerals corresponding to the numerals used in FIGS. 2 and 14 for likecomponents.

Each member M and M' has a pair of grooves 14 and 14' that issemi-circular at its bottom. Grooves 14 and 14' run symmetrically alongboth top and bottom faces of members M (FIGS. 2 and 4). Electric heatingelements 15, with covers 23 (FIG. 5) are tightly received all along thelengths of grooves 14. In applications where easy disassembly of themanifold is desirable (FIG. 3), the grooves 14a and the elements 15a andheater covers are placed on only one face of each members M'. In afurther description with FIGS. 2 and 4, it will be clear that some ofthe heating elements must be removed in order to disassemble members M(FIGS. 2 ad 4). Members M' (FIG. 3) can be disassembled without the needof first removing any of the heating elements.

Member 19 and both members 20 of the manifold in FIGS. 1-5 are made ofmodified stock members M. Member 19 can be called the main conduit forthe resin and members 20 may be called the branch conduits. Whenmanufacturing a manifold of the form in FIG. 1-5, notch or slot (FIG. 4)is machined to a depth of exactly one half the height of the members ata suitable distance from its end so that the upper faces of members Mwill be coplanar and the down faces of members M will also be coplanar.The widths of each nozzle equals the width of the member M at eachjunction, the flat bottom 21 of each notch in each member M abuts thebottom 21 if this notch in the other member M. Longitudinal bore 10 isformed end-to end in each member M. This bore is centered between thesides of each notch: but because it is in the reduced-thickness portionof member M at each notch, the bore is much closer to the unnotched faceof member M or M' than to the opposite face.

A bore 10a is drilled at right angles to the main bore of the manifold 1and 1' for alignment with the bores 11 of nozzles 2. Another bore 10b isdrilled at right angles from the bottom 21 of each notch to thelongitudinal main bore 10 at the center of each notch to thelongitudinal main bore 10 at the center of each notch. Bores 10b of twointersecting members M are aligned with each other; bores 10, 10a and10b constitute resin passages through the manifold. A counterbore at theend of bore 10b forms a seat for a seal 22 between the abutting surfacesof the mating notches of the members M, ensuring that the resin whenunder pressure, does not leak between the members.

End-to-end bores 10 in each member M and M' are closed at the ends withplugs 16 (FIG. 7) which have slanted surface at the back of the head.Pin 17 is used to keep the plug firmly seated against a sealing shoulder16a (FIG. 14) of member M or M', preventing it from rotating as well asfrom being pushed back by the resin under pressure with the passage. Oneside of pin 17 is machined flat, at an angle that is the same as theangle on the back of the plug's head, so that when the pin is pressedwith little force, the inclined plane forces the plug at a 90 degreedirection with a much greater force, sealing the end of the resinpassage. A set screw 18 maintains the pin and the plug under pressure.

Heater covers 23 (FIGS. 5-6) are fitted in the heater groove to allowheat transfer throughout the entire surface of the heating elements.

A socket 24 for the machine nozzle 9 (FIG. 1) is mounted to the manifoldand serves as the main entry port for the molten resin. This socket isheated by virtue of being in close proximity with the manifold.

Bores 11 of nozzles 2 are aligned with the bores 10a of the manifold sothat molten plastic resin can go from the manifold to the nozzlesunimpeded. A seal 25 (FIG. 2) is placed in a counterbore 26 in thenozzle and becomes fixed between the nozzle and the manifold to preventleaks of plastic material.

Instead of a counterbore 26, nozzles can be provided with a sphericalradius 37 (FIG. 9) for use in a single cavity mold, in which case themachine nozzle 9 can be connected directly to the mold nozzle withoutemploying a manifold.

The nozzle 2 is heated by cartridge heaters 27 placed in grooves 28parallel to the resin passage 11. A removable heater cover 29 (FIGS. 10and 11) fits snugly into the groove. The heater cover and the heater arekept under constant pressure against the body of the nozzle by "C"spring clips 30.

A solid torpedo shaped tip 31, made of highly conductive metal, is heldat the extremity of the bore 11 by a restriction or taper 32 at the endof the bore, and is provided with two channels 33 to allow the moltenresin to pass through the nozzle. Pointed tip 34 maintains the resinthat passes into the cavity 8 molten by transferring hat from the nozzlebody. Air gap 35 restricts the flow of heat from the nozzle to the mold.

Cartridge heaters such as the one employed in the nozzle are notoriousfor generating heat very unevenly along their length. The centralsection of the heater has a tendency of becoming much hotter than itsextremities.

To avoid the situation of having the plastic resin degrading at thecenter while it is solidifying at the tip, the nozzle (FIG. 8) isprovided with a plurality of bores 36 that are filled with a liquid suchas water having good heat transfer properties. The end of the bores aretightly capped with plugs 40 and welded to ensure that no liquid escapeswhen the nozzle is heated to high temperatures. Heat is transferred byconduction and convection from the center to the ends of the nozzle;heat transfer is promoted by agitation due to vibration of the apparatuscaused by the mold's opening and closing.

Spring "C" clips 30 have an opening or gap wider than heater grooves 28.When a heater needs to be replaced, the clip is aligned with the grooveand heater cover 29 is removed, exposing the cartridge heater. Theheater can thus be pried out and replaced without the use of specialtools (FIG. 11).

As an alternative method of transferring heat along the shank of thenozzle from the center to the ends, the nozzles can be built with amultiplicity of bores 38 in which rods made of highly conductivity metalsuch as copper or silver are inserted and pressed resulting in anaveraging effect for the heat generated by the heaters 27.

Heater cover 29a can also be manufactured as a section of thecylindrical body of the nozzle (FIG. 12) thus it can be removed withoutprying, once "C" clip 30 is rotated leaving its opening clear of thecover, (FIG. 13).

The presently preferred embodyment of the invention in its variousaspects, which are described in detail above, may be modified andadapted to various forms of molding apparatus by those skilled in theart. Consequently, the invention should be construed broadly inaccordance with it's true spirit and scope.

What is claimed is:
 1. An elongated nozzle for conveying hot fluid resinfrom fluid resin supply apparatus to a mold cavity, said nozzleincluding an elongated nozzle body having an end-to-end central passagefor the fluid resin, and said nozzle body having an external elongatedside surface around the body, multiple elongated channels extendingalong said nozzle body, said channels constituting recesses in saidelongated side surface and being spaced apart around said body,elongated rod-like electrical cartridge heaters received in saidchannels, respectively, and means for releasably confining saidcartridge heaters in said channels, respectively, said means includingat least one retainer member extending around said nozzle body and saidretainer member being movable in relation to said nozzle body intoposition overlying all of said channels and thereby to confine all ofsaid cartridge heaters in said channels, respectively, and said retainermember being positionable to allow removal of any of said heaters.
 2. Anelongated nozzle as in claim 1, wherein said nozzle body has elongatedlongitudinal cavities alternating with said channels around the body andheat-transfer material at least largely filling each said elongatedcavities, said heat-transfer material having greater heat-transferconductivity than the material of said nozzle body.
 3. An elongatednozzle as in claim 2, wherein said heat-transfer material is a metal ofthe group consisting of copper and silver and wherein said body issteel.
 4. An elongated nozzle in claim 2, wherein said cavities aresealed and wherein said material is a heat-transfer liquid.
 5. Anelongated nozzle as in claim 1, wherein heat-transferring heater coversoverlie said rod-like cartridge heaters, respectively, and wherein saidretainer member is effective to confine only such heater cover againstbeing removed whose respective cartridge heater is confined by saidretainer member in its respective channel.
 6. An elongated nozzle forconveying hot fluid resin from hot fluid resin supply apparatus to amold cavity, said nozzle including a nozzle body having an end-to-endcentral passage for the hot fluid resin, multiple elongated channelsalong said nozzle body, said channels being spaced apart around saidbody, elongated electrical cartridge heaters in said channels,respectively, and at least one retainer member extending around saidnozzle body for releasably confining said heating elements in saidchannels, said retainer member largely but incompletely surrounding saidnozzle body and having a gap therein at least wide enough for removal ofone of said cartridge heaters, said retainer member being movable aroundthe nozzle body into a position wherein said gap is arranged in positionto release any one of said cartridge heaters and into other positions inwhich the retainer member secures all of said cartridge heaters againstremoval from said nozzle body.
 7. An elongated nozzle for conveyingfluid resin from fluid supply apparatus to a mold cavity, said nozzlehaving an elongated body having a longitudinal axis and an end-to-endpassage for the fluid resin, and said body having a channel extendingparallel to said passage and opening outward away from the axis of thebody, a rod-like elongated electrical cartridge heater received in saidchannel, an elongated heater cover of proficient heat-conductive metalagainst and along the cartridge heater and the body of the nozzle at theside of the cartridge heater remote from the channel, and a heaterretainer member largely surrounding said body for releasably retainingsaid elongated heater and heater cover assembled to said body of thenozzle, said heater retainer being operable relative to said body intoposition overlying said channel and said heater cover and the heaterreceived in said channel for thereby retaining the heater and its coveragainst removal from the channel, and said heater retainer beingoperable out of position overlying the channel for allowing replacementof the heater.
 8. An elongated nozzle as in claim 7, including at leastan additional channel in said nozzle body extending parallel to saidpassage and opening outward away from said axis, and said nozzleincluding an additional heater cover and an additional elongatedelectrical cartridge heater in said additional channel, said heaterretainer member when in position overlying both of said channels causingretention of both of said cartridge heaters and their covers, and saidheater retainer member being positionable to accommodate removal ofeither of said heaters with its respective heater cover.